1. Field of the Invention
The present invention relates to a copying machine and recording equipment with a computer.
2. Description of the Prior Art
In an electrophotographic copying machine, a photosensitive drum has a photosensitive member consisting of an electrically conductive layer, a photoconductive layer and an insulating layer, the photosensitive member being firmly supported on the peripheral surface of the drum. As the drum is rotated, its surface is uniformly pre-charged (with positive charges, for example) by a primary charger and is scanned with a light image projected from an optical system which in turn is displaced together with or with respect to an original table. Concurrently the scanned surface is discharged by a re-charger with a DC of the polarity opposite to the polarity of the charges imparted by the primary charger. Alternatively, the scanned surface may be discharged with AC. Thus an electrostatic latent image corresponding to the light image may be formed. The latent image is further illuminated or exposed with light so that a high-contrast electrostatic latent image may be formed. Thereafter it is developed into a visible image by a developer with toner. The developed visible image is subjected to a corona discharge with the polarity opposite to the polarity imparted to the toner (for instance, the corona discharge being effected with the negative polarity when the positive pre-charging has been employed) so that the visible image may be more easily transferred onto a copying sheet and then fixed by a heater. After the image transfer, the developing agent mainly consisting of colored particles which remains on the surface of the photosensitive drum is removed and cleaned with a cleaning roller, whereas the remaining charges are removed by a lamp and a corona discharger so that the photosensitive member may be used again. A desired number of copies may be reproduced by cycling the above copying cycle.
In the copying machines of the type described above, a sequential control system has been used for controlling various processing means and especially chargers. In one system used are signals generated by switches which in turn are opened and closed by cams supported on a photosensitive drum. More specifically, upon rotation of the drum, a cam causes a relay to close its terminals, thereby causing the displacement of the original table. When the next cam actuates another relay, a copying sheet feed roller is actuated to feed a copying sheet and so on.
When this cam-and-relay control system is introduced into a retention copying machine or color copying machine, the number of cams and relays is tremendously increased because in this machine processing steps are much greater in number than in the monochrome copying machine. As a result, the control system becomes very complex in construction, the inspection and maintenance becomes very difficult, and the unreliable operation results because of the erratic operations of the switches and relays due to their chattering.
In order to overcome these problems, an electronic digital control system has been introduced in the copying machines so that a sequential control may be attained with logic circuits and arithmetic units. However, the greater the number of steps to be sequentially controlled the greater the number of logic circuits and arithmetic units becomes so that the control system becomes very complex in construction with a very complex wiring arrangement. In addition, these logic circuits and arithmetic units are fixed so that a sequence once set cannot be changed.
Furthermore in the prior art sequentially-controlled copying machines, the sequence is controlled in response to the counting of master clock pulses so that erratic operations tend to occur very frequently due to erratic counting.